1. Field of Invention
The present invention relates to a mask and a manufacturing method thereof. More particularly, the present invention relates to a phase shift (halftone) mask (PSM) and a manufacturing method thereof.
2. Description of Related Art
Generally, the manufacturing process of a conventional mask includes the following steps. First, a quartz substrate whereon a metal layer has been formed is provided. A photoresist layer is formed on the quartz substrate and the metal layer, and by exposing and developing in certain areas, part of the photoresist layer is removed to expose the metal layer thereunder. Next, the exposed metal layer is removed through a dry etching process or wet etching process. Thus, non-transmitting and transmitting patterns are formed on the quartz substrate after the photoresist layer is removed completely. Finally, a transparent pellicle is formed over the substrate, so a binary mask is completed.
Even though the binary mask is widely used in the industry, but slit type mask is generally used upon the reduction of the devices manufacture process. But slit type mask will bring in diffraction effect, which may affect the exposure evenness of the photoresist. Accordingly, there will be unnecessary pattern residue after etching.
A phase shift (halftone) mask can resolve both low accuracy and uneven exposure problems. However, the general manufacturing method for phase shift (halftone) mask is identical to the method for manufacturing a binary mask. First a binary mask is manufactured. After that, a phase shift (halftone) thin film is formed on the binary mask, then a photoresist layer is formed on the mask and the phase shift (halftone) thin film, and then by exposing and developing in certain areas, part of the photoresist layer is removed to expose the phase shift (halftone) thin film thereunder. After that, the exposed phase shift (halftone) thin film is removed through a dry etching process or wet etching process. After the photoresist layer is completely removed, a transparent pellicle is formed, thus a phase shift (halftone) mask is finished. Note that the transmittance of phase shift (halftone) thin film depends on the film material, film thickness, and phase angle.
Even though the phase shift (halftone) mask can resolve the problems of low accuracy and uneven exposure, as etching technology is used in the manufacturing method thereof, when uneven etching occurs on the phase shift (halftone) thin film, the thickness of the phase shift (halftone) thin film on the mask will be uneven. Accordingly the transmittance or phase angles may be different after the light passes through the phase shift (halftone) thin film at different locations of the mask so as to lead to low yield in the lithography process.
Moreover, the manufacturing process of the phase shift (halftone) mask is as follows: forming a layer of phase shift (halftone) thin film on a binary mask after the binary mask is initially formed; performing a lithography process to define the pattern of the phase shift (halftone) thin film; then transferring the pattern to the phase shift (halftone) thin film through an etching process; finally removing the photoresist completely. Compared to the conventional binary mask, there may be more defects when manufacturing the mask due to the complicated manufacturing procedure. Accordingly, the manufacturing cost thereof may be increased.